Oil heater



FIG. 1 is a front elevational view of the oil heater showing our new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof; and

FIG. 5 is a right side elevational view thereof with the left side elevational view being identical. 

The ornamental design for an oil heater, as shown and described. 